Does a Pokémon's potential CP bar scale linearly?

The semicircular bar behind a Pokemon is, in fact, linear.

The lower end of the bar represents some (still unknown) value dependent on the family of Pokemon, and the upper end of the bar represents that Pokemon's current CP cap at your level.

I went ahead and proved the linearality of the semicircle using GIMP. You may see the results here. Note that there may be some error in the numbers due to inaccuracy of my tests (things may not have been lined up quite right).

^(source)